Machines of various kinds often have heavy components that require removal or servicing from time to time. Jacks or similar supporting devices are commonly used for that purpose. The jack may be either a general-purpose hydraulic or mechanical jack of the kind used in most shops or service facilities, or alternatively may be specially designed and built for the particular application. In either case, the jack first is positioned beneath the component to be lifted or supported, and the jack then is raised to engage that component.
It is known to equip jack stands or purpose-built jacks with wheels or rollers, permitting easy placement of a jack beneath a workpiece or machine. Examples of such prior art are seen in U.S. Pat. Nos. 2,751,191 disclosing a mobile jack stand; and in 3,829,063 disclosing an elevated platform installed on a handtruck. Those jacks and jacks stands are suitable for applications such as truck or tractor repair, where no existing structure blocks placing the jack beneath a selected component to be supported by the jack. However, such interfering structure does exist in certain other environments. For example, some industrial machines contain drive gears that are accessible only from the underside of the machine, and that must be removed or adjusted for a proper synchronism from time to time. These industrial machines are supported on the shop floor by posts extending downwardly from the machine frame to mounting pads that engage the floor, and adjacent posts are interconnected by horizontal bracing to provide a rigid support for the operating parts of the machine. This support structure for the machine, and in particular the braces that interconnect the posts and provide structural rigidity for the machine supports, make it impossible to place a conventional jack beneath the machine to engage a gear or other machine component accessible only from the underside of the machine. Custom designing a jack or other tool to fit a particular machine of that kind is prohibitively expensive, given the relatively small market for such custom-designed equipment compared to the relatively broad market for conventional general-purpose jacks. Consequently, removing or adjusting gears or other machine parts in such applications usually is done entirely with manual labor, incurring the risk that a mechanic may be injured by an unsupported machine part that slips while being positioned beneath a machine.